This invention relates generally to fuel rods and other components employed in nuclear reactors. More particularly, the present invention relates to fuel rod cladding tubes and other zirconium-alloy components.
Fuel rods having outer cladding tubes are mounted in support grids of nuclear reactor fuel assemblies. Because of the harsh environment of the fuel assembly where the surrounding water temperature is typically 400.degree. C. and the water has a relatively high pressure, the cladding tube is susceptible to wear and corrosion. At the lower portions of the reactor assembly, the cladding tubes can also be exposed to debris fretting. In addition, severe wear forces can arise at the location of the grid support.
Practitioners in this field are aware that a thin coating of zirconium nitride on a zirconium alloy tube, can dramatically improve wear and corrosion resistance. Such coatings can be applied by any one of a variety of techniques such as ion implantation or plasma spray as disclosed, for example, in U.S. Pat. No. 4,724,016 (Anthony) and U.S. Pat. No. 5,026,517 (Menken et al). More recent attempts include cathodic arc reactive deposition as disclosed in copending U.S. Ser. No. 514,870 (Bryan et al). These techniques, however, exhibit relative strengths and weaknesses, so that none has emerged as clearly superior.